KR20230062070A - Ethod of manufacturing cold-rolled steel sheet - Google Patents

Abstract

The present invention provides a method for manufacturing a cold-rolled steel sheet. The method for manufacturing a cold-rolled steel sheet includes: (a) a step of providing a slab comprising 0.0003-0.0034 wt% of carbon (C), more than 0 and 0.0.3 wt% or less of silicon (Si); 0.05-0.7 wt% of manganese (Mn); 0.02-0.06 wt% of phosphorus (P); more than 0 and 0.01 wt% or less of sulfur (S); 0.002-0.06 wt% of aluminum (Al); 0.01-0.06 wt% of titanium (Ti); and the remainder including iron (Fe) and inevitable impurities; (b) a step of reheating the slab; (c) a step of performing rough milling on the reheated slab; (d) a step of performing finishing milling on the rough-milled slab; (e) a step of winding the finishing-milled slab at the temperature of 620-660℃; and (f) a step of performing cold-rolling on the slab. The purpose of the present invention is to provide the method for manufacturing a cold-rolled steel sheet, capable of optimizing a winding temperature.

Description

Manufacturing method of cold-rolled steel sheet {ETHOD OF MANUFACTURING COLD-ROLLED STEEL SHEET}

The present invention relates to a method for producing a cold-rolled steel sheet, and more particularly, to a method for producing a high-Ti-based cold-rolled steel sheet having excellent surface quality.

In the case of steel sheets for automobile exteriors, demand for beautiful surface quality is increasing as a part responsible for the appearance of the car body. In order to secure the excellent surface quality of cold-rolled steel sheets, each steelmaker is conducting active research to secure technologies not only in the cold-rolling and annealing/plating processes, but also in the preceding steelmaking and hot-rolling processes. In particular, in the case of the hot rolling process, scale is inevitably generated on the surface during the process because high-temperature work is performed. In the case of surface scale, it is a cause of defects that deteriorate the surface quality, so it is removed before rough rolling and finishing rolling, and in the case of scale generated during the winding and cooling process, it is removed through a cold rolling pickling process. However, residual scale may occur on the surface of cold-rolled steel sheet depending on the steel type composition and hot-rolling process conditions. cause of

Korean Patent Publication No. 20140081598

A technical problem to be achieved by the present invention is to provide a method for manufacturing a cold-rolled steel sheet that optimizes a pouring method and a coiling temperature in a rough rolling step of a hot rolling process as a method for improving scale.

Method for manufacturing a cold-rolled steel sheet according to an embodiment of the present invention for solving the above problems is (a) carbon (C): 0.0003 to 0.0034 wt%, silicon (Si): more than 0 and 0.03 wt% or less, manganese (Mn) : 0.05 to 0.7% by weight, phosphorus (P): 0.02 to 0.06% by weight, sulfur (S): more than 0 and less than 0.01% by weight, aluminum (Al): 0.002 to 0.06% by weight, titanium (Ti): 0.01 to 0.06% by weight % and providing a slab consisting of the remaining iron (Fe) and other unavoidable impurities; (b) reheating the slab; (c) rough rolling the reheated slab; (d) finishing-rolling the rough-rolled slab; (e) winding the finished-rolled slab at 620 to 660° C.; and (f) cold rolling the slab.

In the manufacturing method of the cold-rolled steel sheet, the step (c) is characterized in that a scale breaker is applied every time it passes through the roughing rolls.

In the method of manufacturing the cold-rolled steel sheet, in the step (c), the number of passes of the first roughing roll may be three times, and the number of times of applying the scale breaker corresponding to the first roughing roll may be three times. Furthermore, in the step (c), the number of passes of the second roughing roll located at the rear end of the first roughing roll is three times, and the number of times the scale breaker is applied to the second roughing roll may be three times. there is.

In the cold-rolled steel sheet manufacturing method, the step (c) may include rough rolling under conditions of a roughing delivery temperature (RDT): 1020 to 1060 °C.

In the method of manufacturing the cold-rolled steel sheet, the step (b) may include reheating at a reheating temperature of 1180 to 1220°C.

In the cold-rolled steel sheet manufacturing method, the step (f) may include cold rolling under conditions of a cold rolling reduction ratio of 77 to 83%.

In the cold-rolled steel sheet manufacturing method, after the step (e), the interface between the slab base material and the scale layer may include a wustite phase.

According to an embodiment of the present invention, it is possible to implement a manufacturing method of a high-Ti-based cold-rolled steel sheet having excellent surface quality. Specifically, by lowering the hot-rolling coiling temperature and increasing the number of rough rolling scale breakers, scale removal in the cold-rolling pickling process is performed smoothly, thereby preventing defects from occurring.

Of course, the scope of the present invention is not limited by these effects.

1 is a flowchart illustrating a method of manufacturing a cold rolled steel sheet according to an embodiment of the present invention.
2 is a view schematically illustrating a heating furnace and a rough rolling configuration in a method for manufacturing a cold-rolled steel sheet according to an embodiment of the present invention.
3 is a flowchart illustrating an application configuration of a first roughing roll and a scale breaker in the method of manufacturing a cold-rolled steel sheet according to an embodiment of the present invention.
4 is a flowchart illustrating an application configuration of a second roughing roll and a scale breaker in the method of manufacturing a cold-rolled steel sheet according to an embodiment of the present invention.
5 is a photograph of a scale aspect implemented in a method for manufacturing a cold-rolled steel sheet according to a comparative example of the present invention.
6 is a photograph of a scale aspect implemented in a method for manufacturing a cold-rolled steel sheet according to an embodiment of the present invention.
7 is a photograph taken to check whether or not scale occurs on the surface of a cold-rolled steel sheet implemented in a method for manufacturing a cold-rolled steel sheet according to a comparative example of the present invention.
8 is a photograph taken to check whether or not scale is generated on the surface of the cold-rolled steel sheet implemented in the method for manufacturing a cold-rolled steel sheet according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are provided to more completely explain the technical idea of the present invention to those skilled in the art, and the following examples may be modified in many different forms, The scope of the technical idea is not limited to the following examples. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the spirit of the invention to those skilled in the art. Like reference numerals throughout this specification mean like elements. Furthermore, various elements and areas in the drawings are schematically drawn. Therefore, the technical idea of the present invention is not limited by the relative size or spacing drawn in the accompanying drawings.

Hereinafter, the present invention will be described in detail. At this time, in describing the present invention, if it is determined that a detailed description of a related known technology or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted.

In addition, the terms to be described below are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of the user or operator, so the definitions should be made based on the content throughout this specification describing the present invention.

1 is a flowchart illustrating a method of manufacturing a cold rolled steel sheet according to an embodiment of the present invention.

Referring to FIG. 1, a method for manufacturing a cold-rolled steel sheet according to an embodiment of the present invention includes (a) carbon (C): 0.0003 to 0.0034 wt%, silicon (Si): greater than 0 and less than 0.03 wt%, manganese (Mn) : 0.05 to 0.7% by weight, phosphorus (P): 0.02 to 0.06% by weight, sulfur (S): more than 0 and less than 0.01% by weight, aluminum (Al): 0.002 to 0.06% by weight, titanium (Ti): 0.01 to 0.06% by weight providing a slab consisting of % and the remaining iron (Fe) and other unavoidable impurities (S100); (b) reheating the slab (S200); (c) rough rolling the reheated slab (S300); (d) finishing-rolling the rough-rolled slab (S400); (e) winding the finished-rolled slab at 620 to 660° C. (S500); and (f) cold rolling the slab (S600).

The role and content of each component included in the slab for realizing a cold-rolled steel sheet will be described.

Carbon (C): 0.0003 to 0.0034% by weight

Carbon exists as an interstitial solid element and has a very large effect on the strength and texture formation of steel sheets during cold rolling and annealing. When the carbon content is less than 0.0003% by weight, strength may decrease, and when the carbon content exceeds 0.0034% by weight, ductility may decrease.

Silicon (Si): more than 0 and 0.03% by weight or less

Silicon in steel acts as a solid-solution strengthening element, and in this embodiment, the content of silicon is preferably 0.03% by weight or less to secure an appropriate elongation.

Manganese (Mn): 0.05 to 0.7% by weight

Manganese is an effective element for the solid solution strengthening effect, and in particular, sulfur (S) in steel is precipitated as MnS at high temperature to suppress plate breakage and high-temperature embrittlement caused by sulfur during hot rolling. In the present invention, when the content of manganese is less than 0.05% by weight, the effect of increasing strength cannot be obtained, and since sulfur (S) in steel cannot be completely precipitated as manganese (Mn), there is a problem in securing formability. When the content of manganese exceeds 0.7% by weight, workability is adversely affected.

Phosphorus (P): 0.02 to 0.06% by weight

The higher the content of phosphorus (P) in steel, the higher the strength, but the excessive addition of phosphorus decreases the ductility and increases the possibility of brittle fracture, which increases the possibility of plate breakage of the slab during hot rolling, and crystal grains after completion of annealing. As diffusion and segregation into the system become easier, the problem of secondary processing brittleness increases during molding. Therefore, it is necessary to appropriately limit the phosphorus content. In the present invention, since the necessary strength can be secured by the precipitation hardening effect of TiC, the lower limit of P is 0.02% by weight in consideration of the balance between the removal cost and processability of P, and the upper limit of P is 0.06% by weight in consideration of the deterioration of workability. do it in %

Sulfur (S): more than 0 and 0.01% by weight or less

Sulfur (S) is an element that causes red heat brittleness, and its upper limit is determined according to the amount of Mn added to fix S, but since ductility decreases when the S content is high, the upper limit of S is 0.01% by weight in consideration of that. Since the refining cost of steel increases as the S content decreases, it is desirable to manage the content low within the range where operating conditions are possible.

Aluminum (Al): 0.002 to 0.06% by weight

Al works effectively as a deoxidizing element for molten steel, but when added in excess, it adversely affects workability, so the content is limited to 0.06% by weight or less. Since more than 0.002% by weight of soluble aluminum remains in the steel, the actual Al content is 0.002 to 0.06% by weight.

Titanium (Ti): 0.01 to 0.06% by weight

Ti, along with C, is one of the most important additive elements in the present invention. Ti has the effect of forming TiN, TiS nitride and sulfide by combining not only with C but also with N and S. Ti has the effect of increasing strength by precipitation hardening by precipitating TiC during hot rolling and annealing. However, since Ti is an expensive additive, it is advantageous in terms of economy to use as little as possible. Therefore, in the present invention, it is preferable to control the Ti content to 0.01 to 0.06% by weight in consideration of economic feasibility while obtaining the effect of adding Ti.

2 is a view schematically illustrating a heating furnace and a rough rolling configuration in a method for manufacturing a cold-rolled steel sheet according to an embodiment of the present invention.

1 and 2, a step (S200) of reheating the slab 100 having the above-described composition range in the heating furnace 10 is performed. The reheating step (S200) may be performed under the condition of a reheating temperature: 1180 to 1220°C. When the reheating temperature is heated to less than 1180 ° C, time to remove scale and meet the hot rolling finishing temperature may be shortened, and the hot rolling load may increase rapidly, and if it exceeds 1220 ° C, surface quality due to high scale This can be inferior.

The reheated slab is subjected to a scale removal process in the high-pressure slab descaler 20, undergoes a widthwise rolling process in the slab sizing press 30, and is provided to the roughing mill 40.

The roughing mill 40 includes a first roughing roll 43_1 located at the front end along the traveling direction of the slab; a first scale breaker 45_1 disposed near the first roughing roll; A second roughing roll 43_2 located at the rear end along the traveling direction of the slab; A second scale breaker 45_2 disposed near the second roughing roll; includes.

The reason why the roughing roll is composed of a plurality of the first roughing roll 43_1 and the second roughing roll 43_2 is that the roll load is distributed and the thickness of the slab after rolling is easily controlled. The first scale breaker 45_1 and the second scale breaker 45_2 may, for example, perform a function of injecting high-pressure water into the slab 100 to break the scale and push it out of the slab.

3 is a flow chart illustrating an application configuration of a first roughing roll and a scale breaker in a method of manufacturing a cold-rolled steel sheet according to an embodiment of the present invention, and FIG. 4 is a method of manufacturing a cold-rolled steel sheet according to an embodiment of the present invention. It is a flow chart illustrating the application configuration of the second rough rolling roll and the scale breaker in

1 to 4, in the method of manufacturing a cold-rolled steel sheet according to an embodiment of the present invention, the rough rolling step (S300) is characterized in that a scale breaker is applied whenever passing through the rough rolling rolls.

For example, referring to FIG. 3, in the rough rolling step (S300), the number of passes of the first rough rolling roll is 3 times, and the number of times of applying the scale breaker corresponding to the first rough rolling roll may be 3 times. . In this case, the first scale breaker 45_1 may be applied each time the rolling pass passes through the first rough rolling roll 43_1 to remove scale. Specifically, after the first rolling pass is performed in the first rough rolling roll 43_1 (S311), the scale removal process is performed by the first scale breaker 45_1 (S312), and in the first rough rolling roll 43_1 After the second rolling pass is performed (S313), the scale removal process is performed by the first scale breaker 45_1 (S314), and after the third rolling pass is performed on the first rough rolling roll 43_1 (S315), the first The scale removal process is performed by the scale breaker 45_1 (S316).

Meanwhile, referring to FIG. 4 , in the rough rolling step (S300), the number of passes of the second rough rolling roll may be 3 times, and the number of times of applying the scale breaker corresponding to the second rough rolling roll may be 3 times. In this case, the second scale breaker 45_2 may be applied each time the rolling pass passes through the second rough rolling roll 43_2 to remove the scale. Specifically, after the first rolling pass is performed in the second rough rolling roll 43_2 (S321), the scale removal process is performed by the second scale breaker 45_2 (S322), and in the second rough rolling roll 43_2 After the second rolling pass proceeds (S323), the scale removal process proceeds by the second scale breaker 45_2 (S324), and after the third rolling pass proceeds in the second rough rolling roll 43_2 (S325), the second A scale removal process is performed by the scale breaker 45_2 (S326).

Roughing Delivery Temperature (RDT), which is a slab temperature before being provided to the finishing rolling process step (S400) after performing the above-described rough rolling process step (S300), may be 1020 to 1060 °C. In order for the finishing rolling process step (S400) to be performed in the austenite single phase region in the slab having the above-described composition range, it is preferable that RDT (Roughing Delivery Temperature): 1020 to 1060 ° C.

If, in the rough rolling process step (S300), if the number of scale breaker applications performed as many as the number of rough rolling passes exceeds 3 times, RDT (Roughing Delivery Temperature): is lower than the temperature range of 1020 ~ 1060 ℃, so that the finishing rolling process It can be performed in an ideal area rather than a single phase area.

After sequentially performing the rough rolling process and the finishing rolling process, the slab may perform a winding step (S500) at 620 to 660 ° C.

5 is a photograph of a scale aspect implemented in a method for manufacturing a cold-rolled steel sheet according to a comparative example of the present invention, and FIG. 6 is a photograph of a scale aspect implemented in a method for manufacturing a cold-rolled steel sheet according to an embodiment of the present invention. am.

In the process of winding and cooling, the thickness and phase of the scale layer formed on the surface are determined according to the winding temperature.

Referring to FIG. 5, when winding at a high temperature (660 to 720° C.), the surface scale layer is formed thickly, and the interface between the scale layer and the base material is composed of Fe ₃ O ₄ (magnetite) phase.

Referring to FIG. 6, when winding at a low temperature (620 to 660 ° C.), the scale layer is formed thinner than high temperature winding, so that the interface between the scale layer and the base material is composed of FeO (wustite) phase.

Therefore, in the present invention, the scale layer is formed thinly by lowering the coiling temperature and the FeO phase is formed at the interface to prevent defects by controlling the scale to be easily removed in the cold rolling pickling process.

After the winding step (S500), a step (S600) of cold rolling the slab is performed. Cold rolling is a process for making a hot-rolled steel sheet to the final target thickness, and controls mechanical properties such as formability and yield strength of the steel sheet. In this case, cold rolling may be performed under the condition that the cold rolling reduction ratio is 77 to 83%.

Experimental example

Hereinafter, preferred experimental examples are presented to aid understanding of the present invention. However, the following experimental examples are only for helping understanding of the present invention, and the present invention is not limited by the following experimental examples.

Table 1 shows the alloy element composition (unit: weight%) of the specimens of this experimental example.

C Si Mn P S Al Ti Fe 0.002 0.02 0.3 0.04 0.005 0.03 0.04 Bal.

Referring to Table 1, the alloy element composition of the specimens of this experimental example is carbon (C): 0.002% by weight, silicon (Si): 0.02% by weight or less, manganese (Mn): 0.3% by weight, phosphorus (P): 0.04% by weight %, sulfur (S): 0.005% by weight or less, aluminum (Al): 0.03% by weight, titanium (Ti): 0.04% by weight, and the rest iron (Fe).

The composition includes carbon (C): 0.0003 to 0.0034 wt%, silicon (Si): greater than 0 and 0.03 wt% or less, manganese (Mn): 0.05 to 0.7 wt%, phosphorus (P): 0.02 to 0.06 wt%, sulfur ( S): greater than 0 and 0.01% by weight or less, aluminum (Al): 0.002 to 0.06% by weight, titanium (Ti): 0.01 to 0.06% by weight, and the remaining iron (Fe).

Table 2 shows the process conditions and the presence or absence of scale according to the manufacturing method of the cold-rolled steel sheet of this experimental example.

7 is a photograph taken to check whether surface scale is generated on the cold-rolled steel sheet implemented in the cold-rolled steel sheet manufacturing method according to a comparative example of the present invention, and FIG. 8 is a cold-rolled steel sheet manufacturing method according to an embodiment of the present invention. This is a picture taken to check whether the surface scale of the implemented cold-rolled steel sheet is generated.

reheat
Temperature (℃) No. 1
rough rolling
number 2nd
rough rolling
number No. 1
scale
breaker
number of applications No. 2
scale
breaker
number of applications Winding temperature (℃) scale
Occurrence or not Example 1 1,194 3 3 3 3 637 non-occurrence Example 2 1,184 3 3 3 3 639 non-occurrence Example 3 1,205 3 3 3 3 639 non-occurrence Example 4 1,193 3 3 3 3 642 non-occurrence Comparative Example 1 1,195 3 3 One One 677 before/before Comparative Example 2 1,180 3 3 One 4 725 Front Comparative Example 3 1,180 3 3 One 4 726 Front Comparative Example 4 1,208 3 3 2 3 679 Front Comparative Example 5 1,187 3 3 3 One 678 Front Comparative Example 6 1,212 3 3 3 One 679 Front

Referring to Table 2, Examples 1 to 4 satisfy the range of coiling temperature: 620 to 660 ° C, and the scale breaker is always applied whenever passing through the roughing roll (see FIGS. 3 and 4), The number of 1st rough rolling: 3 times, the 2nd rough rolling: 3 times, the 1st scale breaker application number: 3 times, the 2nd scale breaker application number: 3 times. In Examples 1 to 4, it can be confirmed that the surface scale of the cold-rolled steel sheet does not occur (see FIG. 8).

Comparative Examples 1 to 6 are unsatisfactory as they exceed the range of coiling temperature: 620 to 660 ° C, and the scale breaker is not always applied every time it passes through the rolling roll. For example, in Comparative Examples 1 to 4, the number of times the first scale breaker is applied is smaller than the number of first rough rolling, and in Comparative Examples 5 to 6, the number of times the second scale breaker is applied is smaller than the number of second rough rolling. . In Comparative Examples 1 to 6, it can be confirmed that the surface scale of the cold-rolled steel sheet occurs (see FIG. 7).

According to the above-described experimental example, it can be seen that the degree of residual scale in the final hot-rolled coil varies according to the number of injections of the scale breaker and the coiling temperature in the rough rolling process in the production of high Ti-based hot-rolled steel sheet.

When the number of water injections is low or the coiling temperature is increased, residual scale occurs in hot rolling, which causes scale defects to occur throughout the entire length of the final cold rolled coil. It can be confirmed that the occurrence of defects can be prevented by smoothly removing the scale in the pickling process.

Although the above has been described based on the embodiments of the present invention, various changes or modifications may be made at the level of those skilled in the art. As long as these changes and modifications do not depart from the scope of the present invention, it can be said to belong to the present invention. Therefore, the scope of the present invention will be determined by the claims described below.

10: heating furnace
20: high pressure slab descaler
30: slab sizing press
40: roughing mill
43: roughing roll
45 : Scale Breaker
100: slab

Claims (8)

(a) Carbon (C): 0.0003 to 0.0034 wt%, silicon (Si): greater than 0 and 0.03 wt% or less, manganese (Mn): 0.05 to 0.7 wt%, phosphorus (P): 0.02 to 0.06 wt%, sulfur ( S): more than 0 and 0.01% by weight or less, aluminum (Al): 0.002 to 0.06% by weight, titanium (Ti): 0.01 to 0.06% by weight, and the rest iron (Fe) Providing a slab consisting of other unavoidable impurities;
(b) reheating the slab;
(c) rough rolling the reheated slab;
(d) finishing-rolling the rough-rolled slab;
(e) winding the finished-rolled slab at 620 to 660° C.; and
(f) cold rolling the slab; including,
A method for producing cold-rolled steel sheets. According to claim 1,
The step (c) is characterized in that the scale breaker is applied every time it passes through the roughing rolls,
A method for producing cold-rolled steel sheets. According to claim 2,
In the step (c), the number of passes of the first roughing roll is 3 times, and the number of times the scale breaker is applied to the first roughing roll is 3 times.
A method for producing cold-rolled steel sheets. According to claim 3,
In the step (c), the number of passes of the second roughing roll located at the rear end of the first roughing roll is 3 times, and the number of times the scale breaker is applied to the second roughing roll is 3 times. doing,
A method for producing cold-rolled steel sheets. According to claim 1,
Step (c) includes rough rolling under conditions of RDT (Roughing Delivery Temperature): 1020 ~ 1060 ° C.
A method for producing cold-rolled steel sheets. According to claim 1,
The step (b) includes reheating at a reheating temperature of 1180 to 1220 ° C.
A method for producing cold-rolled steel sheets. According to claim 1,
The step (f) comprises the step of cold rolling under the condition that the cold rolling reduction ratio is 77 to 83%.
A method for producing cold-rolled steel sheets. According to claim 1,
After the step (e), the interface between the slab base material and the scale layer comprises a wustite phase,
A method for producing cold-rolled steel sheets.

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